Floating cover for sewage digesting apparatus



y 29, 1952 J. H. WIGGINS ETAL 2,605,014

I FLOATING COVER FOR SEWAGE DIGESTING APPARATUS Filed Oct. 26, 1949 3 Sheets-Sheet 1 INVENTORS. JOHN H. WIGGINS JOHN W.ALLEN ATTORNEY July 29, 1952 J- H. WIGGINS ETAL FLOATING COVER FOR SEWAGE DIGESTING APPARATUS Filed Oct. 26, 1949 3 Sheets-Sheet 2 f INVENTORS,

* JOHN H. WIGGINS JOHN W.ALLEN H q ATTORNEY 3 Sheets-Sheet 5 J. H. VYIGGINS- ETAL FLOATING COVER FOR SEWAGE DIGESTING APPARATUS Filed Oct. 26, 1949 July 29, 1952 INVEMTORS. JOHN H.WIGGIN5 ATTORNEY Patented July 29, 1952 JohnH. Wiggins and ohn AllemChicago, ;v a 'said %l1en assigno'r to saidylliggins f Application October 26, 1949, Serial No. 123,762

' .IIhis invention relates to apparatus of the general type or kind that comprise a tank adapted to hold a liquid material or substance that is being stored or processed, and a cover or closure for said tank that normally floats upon and is supported by the-liquid in the: tank. We have herein, illustrated our invention applied to or embodied in a sewage digesting apparatuagbut we wishgit to be understood that our invention isapplicable to apparatus usedfor other purposes than digesting sewage: i,

;, fIhe main object of our invention is toreduce the cost and improve the operation of apparatus of the-general type orkind above mentioned";

One of the novel features or. characteristics of our improved;apparatusis that its floating cover comprisesaflexible or; limber deck portion combine wi h a i annu r,,;'per p era1 n r:

- tion havi ga. built-inlgad member constructed will be maintained in intimate contact with the liquid and in anlnclined position sloping up war dly towards the center oi the cover. I Another novelieature of our improved apparatus isthat theperipheral portion of. the'floating cover of same is constructedin the form of a ring girder, composed of a fabricated, metal part and a molded load member of; concrete,.or the like, combined in sucha way that when the substance of which said loadrmember is constructedhardens or sets, said load member will co-act with the fabricated metal part to carrycompressionloads. 1 Another; novel feature ot our'improved apparah s s. a the builtgil load, m r. nad o to i rea i ehaw sht andb bi com.- es n s ise up: n th pe p eral, or o oft e floa in cov lso. act as ins la or that th r n: 7

soia m (craze-gel" its,

the top side of the cover is adapted to receive and hold a body-of waterathat constitutes a load whichincreases the weight of the, cover sufficiently to maintain the cover inintimatecom tact with the sewagein the tank, therebytending to prevent-a thick cake oforganic matterirom collecting between the cover and the liquid portion of the sewage, and the bottom surfaceof the cover is of such shape or form that gases evolved from the sewa e, have a natural tendency to flow towards a gas collecting chamber at thecenter of the cover. r v Another novel feature consists of a floating cover of the kind-referred to in .the preceding paragraph having provision for enabling. the

water load on the 'top side of theycover tobe replenished by practically clear water in the tank fromthe solid particles oi, the

Sewage,

And still another desirable feature of our improved apparatus is that snow or rain which falls on the floating cover will not injuriously afiect the operation of the apparatus, and when the tank is emptied and the cover moves downwardly onto a stationary supporting means or structure on the interior of thetank, the water load on All the covercan eithermanually or automatically be drained ofi the cover.. Other desirable feae tures orcharacteristics-of the apparatus con: stituti'n'g our invention will be hereinafter pointed out. v r

Figure 1 ofthe drawings illustrates a sewage digesting apparatus embodying one form of our invention, showing the cover floating on the liquid in the tank, the left 'handhalf ;-of said figure being in vertical, transverse section, and the right hand half being in elevation. r a

Fi ure shQWS the cove t n v on helsunporting structure-inside of the tanlc the left :hand half of said; figurebeing :vertical, transverse section and the right hand half in top. plan 7 I Figure 3 15 an enlargedjsectional view of one of, the overflowv wells on the decl; portion ofthe floating cover shown in Figure s l and ;2, and Figure d'illustrates another forrn of ourinven-l tion, said-figure being= ;a.half,, vertical transe verse-sectional-view. g; v

In Figures 1. and -2, the reference character- A es na th an of t ea pa tu swhiqh is adapted-to-hold the sewageland B designates ,-as

an entirety the floating cover, the tank A being herein illustrated as constructed of concrete and provided with a vertical side wall of circular form. The cover B, which floats on the sewage in the tank A, can be constructed in various ways, without departing from the spirit of our invention, so long as it comprises a flexible deck portion of circular form, whose underside is in direct contact with the sewage or other liquid in the tank, and a stiff, annular load member constructed of concrete or the like, attached to the peripheral edge of said deck portion so as to maintain said deck portion in an inclined position sloping upwardly and inwardly from the peripheral edge. In the particular form of our invention shown in Figures 1 and 2, the cover comprises-the following elements, i. e., a center pontoon C of circular form, a peripheral pontoon D of an,-,

nular form surrounding the center pontoon and arranged in close proximity to the side wall of the tank, and a flexible single deck portion E bridging the space between said pontoons .and

rigidly connected to same, preferably at the lower ends of said pontoons, said deck portion being constructed from metal plates. The center pontoon C consists of a fabricated metal structure that is reinforced and strengthened by a plurality of radially-disposed trusses F, the top of said pontoon preferably having a downward pitch or slope from its center towards its outer edge, and thebottom of said pontoon preferably having a slight upward slope from its outer edge towards its center. At the center of the pontoon C there is a gas dome or gas collecting chamber G, whose lower end is open, so that gases which are evolved from the sewage in the tank A, can collect in the chamber G, and subsequently, escape from same through a gas-eductor pipe H that leads to the atmosphere, or to a point where the gases are utilized as a heating medium.

The peripheral pontoon D; is of novel construction, in that it is provided with a built-in load member, which, in addition to adding considerable weight to said pontoon and causing it to float in the liquid at a level lower than the degree of submergenceoi said pontoon in the absence of said load member, also acts as a stiffening member that absorbs compression stresses set up in the pontoon D when the apparatus is in use. Due to the particular way said load member is-located, said member also acts as a heat insulating medium for the submerged portion of the pontoon D in contact with the liquid on which the cover B of the apparatus floats. In the apparatus herein illustrated the peripheral pontoon D is constructed of metal plates fabricated in such a way as to produce an annular girder of substantial box-shape in cross section, and on the interior of said hollow girder, there is located a load member D formed from a relatively heavy substance or material that can be poured into the pontoon D while in a liquid or plastic stateand which subsequently will solidify 0r harden into a-dense, flat slab of great weight and substantial thickness. Wepre'fer to form the load member D from concrete, due to the low cost of concrete and the ease with which-it can be installed in and combined with the metal shell of the pontoon D, but said load member can be formed of various other substances or materials without departing from the spirit of our invention. As shown in the drawings, the pontoon D is'provided with a plurality of vertically disposed internal bulkheads I arranged in spaced relation around the circumference of said pontoon. Said bulkheads I are rigidly attached to the top wall and to the side walls of the pontoon, but the bottom edges or lower ends of said bulkheads terminate short of the bottom wall of the pontoon, so as to produce a space in the lower portion of the pontoon that extends continuously around the circumference of the pontoon and which is not broken up or divided into sections by the bulkheads I. It is this continuous or unbroken space in the pontoon D that receives the load member D, and in constructing said load member, it is made of such thickness that the lower end portions of the bulkheads I will be imbedded in the top portion of the load member. To efi'ectively tie the load member to said bulkheads, the lower end portions of said bulkheads are provided with lugs or projections that. become imbedded in the material of which the load member D is constructed when said material sets or hardens, thereby causing the load member and bulkheads to become interlocked with each other. The load member D is also preferably interlocked with or tied to the bottom wall and the side walls of the pontoon D by lugs or projections on the inner surfaces of said walls that become imbedded in the load member during the operation of pouring, molding, orcasting the self-hardening plastic sub stance of which the load member is constructed.

Such a pontoon is easy to build and inexpensive to construct; it will float at a lower level in the sewage or sink into the sewage to a depth in excess of the degree of submergence of the pontoon in the absence of the load member D, thereby exerting a downward force on the peripheral edge of the deck portion E that deflects said deck portion and maintains it in a sloping position that enhances the flow of gases on the underside of said deck portion and on the underside of the peripheral pontoon, towards or into the gas dome G at the center of the floating cover of the apparatus; it is stronger-and of greater rigidity than an annular pontoon of conventional construction, inasmuch as the load member D consists of a dense slab of rigid material of substantial thickness, interlocked with the metal top, bottom, and side walls of the pontoon in such a way that it absorbs stresses set up in the pontoon when the apparatus is in use; and it has th further desirable characteristic of retarding the escape of heat employed to speed digestion of the sewage, dueto the fact that the load member D constitutes a heat insulating medium for the entire area of the bottom wall of the pontoon upon which said load member is superimposed and interlocked with.-

In order to efiectively prevent a thick cake of organic matter from forming between the underside of the cover B and the liquid on which the cover floats, a water load a: is carried onthe cover 8 so as to increase the'weight of said cover. In the apparatus herein illustrated said water load is confined in an annular water trough on the top side of the cover B, formed by the'deck portion E and the side wall portions" of the center pontoon C and peripheral pontoon D that project upwardly a substantial distance above the top surface of said deck portion." Said water loads is prevented from rising above a certain level, and hence, is maintained at a predetermined approximate weight by meansof a plurality of overflow wells J- onthe topf sidepf the deck portion E, equipped with water outlets K that project downwardly aconsiderable distance into the sewage and discharge rain water or snow water into the tank, said water'outlets prefer ably being of such length that the lower ends of same terminate inpractically clear water. The water'outlets- K can; either be formed'by rigid metalpipes provided at their lower endswith bafiies' K disposed was to prevent sol'idparticlesinthe sewage from rising in said pipes, or said water outlets may be formed by metalpipes projecting downwardly from the overflow wells J and having their lower ends attached to flexible extensions that extend downwardly to a point in' relatively close proximity to; the bottom of th'tank A. Due to the fact that the waterout lets K from the overflow wells on the deck portion E terminate in tank water that is substantially clear and free from solid particles of sewage, on or more of the overflow wells can be provided at its lower end with a water orifice or passageway, disposed so that in the event the water ess a: on the deck portion'E falls below a certain approximate level, clear water in the tank A will rise through" one or morej ofjrthe water outlets K and discharge ontothe deck portion E', through the above mentioned water discharge orifices or passagewaysin the overflow wlls', thus replenishing the water madon said deck portion, this feature of ourapparatus being of considerable value in localities where'water is scarce. Instead of using an uncontrolled water orifice or passageway for adding water to the Water load an on the deck portion, we prefer to equip-oneor more of the overflow wells J with a valve L mounted in the lower end portion of the side Wall of the well at such a point thatwater which rises in the overflow pipe leading from the well canpass, practicallydirectly, from the overflow pipe onto 'theideck portion Inrthe event such a valve L is nornially set in itsr open position, the water loads: on the top side .of the deck portion E will automatically b main- .tained at the ideal height, depth or'level. Also such an orifice orsy alve facilitates drainage or discharge of water from the top side of the deck portion B when the floating cover B of the apparatus comes to rest on its supporting, structure inside of the tank, duringthelpperatiori o-fiemptrin ai t P r lt W f m manually-operated drain valves P are mounted -;in thedeck portion shown in Figiire 2} so as to facilitate the discharge of the water-load :cwhen the cover is resting on the supporting structure in the tank. In the apparatus herein illustrated the supporting structure just referred to comprisesa tower Mof ske emmnke construction at the center of the tank A which is adapted tosupport the center'pontoon when the cover is not floating, and a plurality of inwardly-projectifibiack'e'ts O on the side wall of said tank that are adapted to support the annular, peripheral pontoonD.

we prefer to construct the floating cover B of the apparatus so that the area of the two pontoons C and D constitutes 50% of the total area of the cover, and thearea of the deck portion E constitutes 50% of the total area of said cover. The drain wellson said desk portion are "so proportioned and arranged that under normal conditions when the cover is floating on] the Iiduid in the tank A, the water load seen the .dck' portion E will be of such weight that the center pontoon'C will carry'itself and also the deck portion E, and the peripheral pontoon D will carry itself. If the weight of the water load oh, the deck portion were too little,said deck portioh wouldexert an upwardlift on the peripheral pontoon D, thereby causing part of the weight tank on which the cover fioats,-exaotly carries the waterload at on the deck portion 13'. To attainan operating gas pressure of 7-"'-'IlZ" 20,- the deck portionmustbe loaded with water until none of thawei'g-ht of the peripheralporitoori D 'i'scarried'by other parts crimeiidating' cover. this case the deck porti'on E is a substantially straight line andthe entirestructure'is in stable equilibrium.' As the weight orthebuilt-in load-member D'- in the peripheral pontoon, said member is s o proportioned that when the cover is floating; said lead member-'e-Xerts-a-sufiicient downward force on the peripheral edge of the deck portionE to impart an upward and inward slope to said deck' portion, whereby gases ont'he underside of th-e cover evolved from the sewage, have afnaturaltendency to flow towards thegas dome Gin the center pontoon C. Wealso prefer to form the bottom of saidcenter pontoon so that it has a slight upward slope from its periphery towards its center. I

The overflow wells J on the deck portlonEare preferably designed or proportioned so that the weight of thewater load as is not sogreat as to deflect the peripheral edge of the deck portion'E and thus destroy the ideal slope or angle at which said deck portion is maintained by the built-in load member 'i'n' the peripheral pontoon. In the apparatus herein shown the side walls of said overflow Wells are made about 2 higher than the level of the ideal water load x cnthe deck portion. .The tank water admitted" to said over,- flcw wells bythe outlet pipes K, rises on tha inside for the wells J only 1', for a 2" rise of the body'of'w'ater a: on the deck portion, because said deck portionconstitutes.only one half of the total'ajr'ea ofithe floating. cover B. Therefore, rain will automatically drain off the cover into the'ta'nk. In case of snow, any" amountthat'falls' onto the deck portion E will displace the water thereon, and hence, not increase that load beyond 7 the overflow point. If snow collectso'n the'top's of the pontoohs c and D, it would require 20" of dry snow (10 per 1 H 20) before the tank water wouldflowont'o the deck portion It the Water load xon the deck portion had a solid covering of ice,'the tank water inside the overflow wells J would probably be frozen. If it is the water on the topside of the deckportionE will flow into the tank through the overflow devices located adjacent the periphery of the center pontoon, until most of thewater load x on the deck portion has drained into the tank. As previously stated, one or more hand drains P are provided so that all of the deck water can be discharged into the tank. Thus, the maximum live load is the snow load. The apparatus, as preferably designed, however, carries the snow load, plus the water that does not drain oif the cover B automatically.

In covers of relatively small size the center pontoon previously referred to can be omitted. Accordingly, Figure 4 of the drawings we have illustrated another form of our invention consisting of a floating cover composed of a flexible or limber deck portion E of annular form, a single pontoon D of annular form attached to the peripheral edge of said deck portion and provided with a built-in load member D ofthe same construction and functional characteristics as the load member ofthe peripheral pontoon of the apparatus, shown in Figures 1 and 2, and a vertically-disposed, tubular member C at the center of the cover, open at its lower end and attached to the inner edge of the deck portion E 9 so as to serve as a gas dome or gas collection chamber G the upper end of said tubular member being closed by a gas-tight cap H. Instead of permitting rain water or the like to collect on the cover, we use a rain shield or weather roof I2 to bridge the space between the peripheral pontoon D and the center tubular member C and we make said weather roof of such shape that rain which falls on same will drain from the peripheral edge of said roof onto the top of the peripheral pontoon D which is inclined downwardly so as to discharge rain and snow into the annular space between the peripheral edge ofthe cover and the side wall of the tank A.

The weather roof I2, which preferably is substantially cone-shaped, is of rigid construction and is herein illustrated as being supported by radially-disposed, downwardly-inclined rods i3 attached at their inner ends to the upper end of the center tubular member and attached at their outer ends to the inner edge portion of the peripheral pontoon D When the cover is not floating on the liquid in the tank, as shown in broken lines in Figure 4, it is supported by brackets O on the side wall of the tank and a towerM located at the center of the tank, proportioned and arranged so as not tosubject the rigid weather roof I2 to strains.

When the cover is floating, as shown in full lines in Figure 4, the weight of the concrete load member D in the peripheral pontoon D causes the peripheral portion of the cover to sink into the liquid to a point or level lower than the degree of submergence of said peripheral portion in the absence of said load member, thereby maintaining the flexible deck portion in an upwardly-sloping position, and causing gases that collect on the underside of the cover to flow into the gas dome G at the center of the cover. Thus, the cover is supported by the buoyance of the peripheral pontoon D and by the extra submergence of (over its own weight) the deck portion E When the cover is not floating, the

center tower M holds the bottom edge of the the tank.

in the same relative elevations as when the-cover is floating, with the result that the weather roof is not subjected to strainsthat tend to flexor injure it. Such a-cover has the samedesirable characteristics as thecovershown in Figures 1 and 2, so far as the cost and accomplished re: sults of the peripheral pontoon are concerned. and in practice, would be used in a'pparatusof such size that it is not necessary to provide the cover with a center pontoon. v

Having thus described our invention, what we claim and desire to secure by Letters Patent is: r

1 An apparatus comprising a tank that is adapted to hold a liquid or liquid-like substance that isbeing stored or processed, and a cover for said tank formed by a floating roof that rests upon the liquid in the ank and moves vertically, duetochanges in the level of the liquid, said roof comprisinga flexible deck having a peripheral portionthat comprises a' load membergformed from a'relatively heavy moldable material that exerts a suflicient downward force on said peripheral portion to maintain the'flexible deck in an inclined position sloping upwardly andinwardly towardsthe center of the roof, said peripheral portion being constructed in the form of a fabricated metal girder of substantially box shape in cross section provided with bulkheads, and

said lead member being constructed in the form of a continuous ring-shaped slab disposed in superimposed relation with the bottom wa'll of the girder and interlocked with the side walls, bottom wall and lower end portions of the bulkheads of the girder.

2. An apparatus, comprising a tank adapted to holda liquid or liquid-like substance, a floating cover for said tank provided adjacent its center 'in such a position as to induce the flow ofgases ,on the underside of said cover, into said gas-collecting chamber. a

3. An apparatus of the kind described in-claim 2, provided with meansfor discharging the water load on the deck portion into the interior of j 4. 'An apparatus of the kind described in claim 2, in which said deck portion is provided with a drain device, consisting of an overflow well projectingupwardly from the deck portion and provided at its lower end with an orifice, and a conduit leading from the lower end of said well and terminating inside of the tank at a point a substantial distance below the level of the which the cover floats;

5. A floating cover for a tank that holds a liquid or liquid-like substance, composed, of a center pontoon, an annular, peripheral pontoon provided with a built-in load member disposed on the interior of said pontoon and extending continuously around the circumference of same in contact with the bottom wall of said pontoon, and a flexible deck portion bridging the space between said pontoons and rigidly attached to the uid lower ends of same, said pontoons and deck portion being so proportioned and arranged that when the cover is floating with a water load of the proper weight on said deck portion, the center pontoon will carry its weight and also the weight of the deckportion, the annular pontoon will carry its weight and also the Weight of said REFERENCES CITED The following references are of record in the file of this patent:

Number 10 Number 10 UNITED STATES PATENTS Name Date Downes June 11, 1929 Fischer Sept. 6, 1938 Wiggins Aug. 19, 1947 Wiggins Nov. 11, 1947 Cranmer Nov. 1, 19 4 9 FOREIGN PATENTS Country Date- Great Britain Feb. 5, 1945 

